This research was performed with the aim of determining sibling relationships of individuals with parents who have mental illness. Material and Methods: This research was a qualitative study using phenomenological design. A total of 14 individuals, determined with the purposeful sampling method, with a parent who had mental illness for at least 20 years, with at least 1 sibling and from 7 family pairs were interviewed. Data were collected with a semi-structured interview form and analyzed with the content analysis method. Ethics committee permission and individual consent from participants were obtained. Results: The mean age of participants was 31.64±4.95 years, including 8 women and 6 men. Parents of 4 of the participants had schizophrenia, 6 had bipolar and 4 had depression diagnosis. The mean duration of mental illness in parents was 26.85±4.18 years. In the research, 2 main themes and 6 sub-themes emerged. The themes were determined to be solidarity (sharing, emotional support, personal development) and conflict (shifting roles, heavy burden, broken ties). Conclusion: The results of this study reveal the status of sibling relationships among individuals with parents who have mental illness. It appears that siblings living with parents who have mental illness is a process ensuring solidarity like sharing, emotional support and personal development, while also involving conflict from many perspectives like shifting roles, heavy burden and reduced sibling relationships. These results may be used to develop integrated mental health services by assessing sibling relationships of individuals with parents who have mental illness.